Casters are commonly mounted to transport vehicles, such as carts, trailers, trucks, or dollies, and allow for rolling movement of the transport vehicle along a ground surface. Conventional casters generally include a horn (also referred to as a yoke) having a pair of legs that extend downwardly and support a caster wheel that rolls along the ground surface.
Casters may be designed to rotate, or “swivel,” about a vertical axis (termed “swivel” casters), or they may be fixed (termed “rigid” casters). Conventional swivel casters generally include a horn that is rotatably coupled to a swivel plate, which in turn is mounted to a vehicle, such that the horn and caster wheel may swivel about a vertical swivel axis relative to the swivel plate and the vehicle. This swiveling action enables the caster wheel to change direction while rolling, thereby allowing an operator to turn or otherwise steer the vehicle. In contrast, rigid casters generally include a horn that is rigidly attached to the vehicle via a mounting plate, such that the caster wheel does not swivel. Transport vehicles may be fitted with one or more swivel casters and one or more rigid casters, depending on the application and vehicle design. In a common arrangement, a vehicle may include swivel casters on a rear operator-end of the vehicle, and rigid casters on a front end of the vehicle. For improved vehicle maneuverability in tight spaces, the vehicle may be provided with swivel casters at both vehicle ends, as often seen on grocery carts, for example.
On conventional swivel casters, the wheel is mounted with its axle such that the horizontal wheel axis is offset laterally from the vertical swivel axis. In other words, the wheel is mounted such that the vertical swivel axis does not pass through the horizontal wheel axis. During vehicle movement, this offset enables the wheel to change direction as needed in order to position itself behind (or “trail”) the swivel axis, thereby maintaining proper self-alignment with the direction of travel of the vehicle.
When the vehicle reverses its direction of travel, the caster wheel must swivel a full 180 degrees through an arc to a new trailing position in order to realign itself with the new direction of travel of the vehicle. As the wheel swivels, it passes through a point in its arc at which the wheel is momentarily perpendicular to the new direction of travel. At this point, the wheel frictionally drags across, or “scrubs,” the floor, thereby requiring an increase in force applied by the operator to the vehicle in order to complete the vehicle turn. This “scrubbing” undesirably increases stress on the swivel bearing components and the wheel tread, and accelerates their wear.
To address this shortcoming of conventional swivel casters, attempts have been made to produce a swivel caster in which the wheel is able to slide horizontally, relative to the swivel plate, between first and second trailing positions arranged on opposing sides of the swivel axis. The objective was to eliminate the need for the caster to swivel when reversing direction, and instead achieve a change in direction by relying solely on a horizontal repositioning (i.e., sliding) of the wheel relative to the swivel plate and vehicle. However, these prior attempts have failed to produce a design having a slide mechanism that operates effectively when under compressive radial load (i.e., along the swivel axis), or that is properly activated so as to truly minimize the degree of swiveling, and thus scrubbing, of the wheel during a change in direction of the vehicle. For example, the wheel of known swivel casters having a slide mechanism would prefer to fully swivel, rather than slide, to a new trailing position if there is even a slight misalignment between the sliding axis of the slide mechanism and the new direction of travel of the vehicle (e.g., a direction of force exerted on the vehicle by an operator).
Accordingly, there remains a need for improvements to known swivel casters to address the shortcomings described above.